PRINCIPAL ELEMENTS OF THE TECTONICS OF THE LENINSKY COAL DISTRICT OF KUZBASS

Yu. N. POPOV

(Submitted by the Department of Geology and Exploration
of Mineral Deposits)

The systematic and detailed study of the tectonics of Kuzbass, begun by M. A. Usov, continues at the present time as well. In the last two or three decades, the tectonics chiefly of complexly dislocated districts has been studied, especially that of Prokopyevsk–Kiselevsk; and this is not surprising, since M. A. Usov [7] indicated that “Kuzbass is a favorable object for the study of tangential disjunctives,” and the latter are most widely represented precisely in the Prokopyevsk–Kiselevsk district. The principal method for studying tectonic structures was the generalization of the results of direct observations in the mine workings of operating mines, with the use of data from geological-exploration work. Such an approach to solving the problems posed fully justified M. A. Usov’s words that “questions of mine tectonics are important not only for solving practical problems, but also theoretical ones.” In the Prokopyevsk–Kiselevsk, Anzhero, and Kemerovo districts, the question of the morphology and localization of small disjunctives and folds was, in general, resolved, which is extremely important for conducting exploration and mining operations.

Beginning in the summer of 1961, a group of research workers of the Tomsk Polytechnic Institute, together with production geologists and under the direction of V. Ya. Koudelny, began to study the tectonics of the Leninsky coal district of Kuzbass. This was necessary in order to understand the previously little-studied tectonics of the central, comparatively less dislocated part of Kuzbass, represented by deposits of the Kolchugino Series \((P_1—P_2)\). The resolution of this question should also shed additional light on the understanding of the tectonics of Kuzbass as a whole.

M. A. Usov devoted serious attention to the study of the tectonics of the Leninsky district. In the first period of study, he considered the principal structural element of the district to be a large anticlinal fold [5]; however, already in 1929 [6] he gave a correct assessment of the tectonics of the district and pointed to the presence here of a large disjunctive. The errors found in the views on the tectonics of the district held by a number of other researchers are connected with the fact that all exploration and mining operations of that time were concentrated within the mine field. At present, owing to the broad development of coal mining within the district (the “Leninugol” trust is one of the largest in the basin) and the extensive coverage of the district by detailed geological-exploration work, ideas about its tectonic structure have also changed.

And the discovery of new promising areas and the forthcoming mine construction make the study of the tectonics of the district and the prediction of the structure of the fields of mines under construction and design highly urgent from the standpoint of production.

Situated in the central and southeastern part of the belt of coal-bearing deposits of Kuzbass, whose structure was formed mainly as a result of the complex process of tectonic dislocations at the junction of Salair and Kuzbass, which were also reflected in the basement of the latter, the Leninsky district is characterized by less intense tectonics than the Prokopyevsk–Kiselevsk and Bachatsky districts, which directly adjoin Salair. This circumstance was the reason why, in the tectonic zoning of the basin, a subzone of “linear gentle folding” was distinguished within the “Prisalair zone of linear folds and faults.” The names of the zone and subzone are given here according to the scheme of tectonic zoning of Kuzbass proposed by A. A. Belitsky and E. M. Pakhom [2], which is the most recent, compiled with consideration of the schemes of other authors, and characterizes the morphological and genetic features of dislocations, as well as the metamorphism of coals and rocks. With the exception of certain debatable questions of terminology, it is entirely acceptable at the present stage of study of the basin’s tectonics.

The most essential feature of the tectonics of the Leninsky district should be considered the presence within it of a number of large thrusts parallel to the southwestern boundary of Kuzbass, which has conditioned the block (imbricate) structure of the district. Within the latter one may distinguish five imbricate slices (from southwest to northeast): the Chertinskaya, Belovskaya, Leninskaya, Gramoteinskaya, and Uropskaya (Fig. 1). The Chertinskaya slice is situated between the Afonino–Kiselevsk thrust in the southwest and the Kutanov thrust in the northeast; the latter bounds the Belovskaya slice on the southwest. The Belovskaya slice, in turn, is separated from the Leninskaya slice by the Kilchigiz thrust. The boundary between the Leninskaya and Gramoteinskaya slices is the Zhurinsky thrust. The Gramoteinskaya slice is separated from the Uropskaya by the Vinogradovsky thrust. The northeastern boundary of the Uropskaya slice has not been established and, evidently, lies beneath the cover of Jurassic deposits, which overlie the deposits of the Kolchuginsky Series with a significant angular unconformity. The disjunctives delimiting the slices are large thrusts, parallel to the boundary of Kuzbass with Salair. The average distance between them is 5–6 km.

The next feature of the district’s tectonics is the brachyfold character of first-order plicative dislocations within the slices. The brachyfolds are elongated along the slices and have, in general, gentle dips. Thus, within the Chertinskaya slice the Chertinskaya and Ustyuzhaninskaya brachysynclines are developed. In the Belovskaya slice the principal plicative structures are the Belovskaya and Nikitino-Kasminskaya brachysynclines; in the Leninskaya—the Leninskaya syncline; and finally, in the Gramoteinskaya—the Egozovo-Krasnoyarskaya brachysyncline. Thus, the leading fold forms in the Leninsky district are brachysynclines. The anticlines separating them are considerably smaller in size and are partly destroyed by the large thrusts that form the boundaries of the slices. These disjunctives are confined mainly to the closures of the anticlines and their northeastern limbs, as a result of which, by the present time, in some brachysynclines only the northeastern limbs have been preserved.

A characteristic feature of the tectonics of the Leninsky district is also that, within the slices, it is generally not marked by great intensity or diversity. The coal-bearing deposits in most of the explored

Fig. 1. Schematic geological map of the Leninsky district of Kuzbass (Kuzbassuglegeologiya Trust, 1961):
a — conglomerate suite; b — Erunakovskaya suite; v — Ilyinskaya suite; g — Kuznetsk suite; d — suite boundaries; e — outcrops of coal seams beneath overburden; zh — disjunctives; z — mine shafts: 1 — E. Yaroslavsky Mine, 2 — “Zhurinki 3,” 3 — E. Yaroslavsky Mine (old), 4 — S. M. Kirov Mine, 5 — “Novyi,” 6 — “Komsomolets,” 7 — “7 Noyabrya,” 8 — “Polysaevsky-1,” 9 — “Polysaevsky-Severnyi,” 10 — “Polysaevsky-II,” 11 — “Polysaevsky-III”; i — numbers indicating the following structures on the map: 1 — Ustozhanikhinskaya syncline, 2 — Novorossiiskaya anticline, 3 — Kasminskaya syncline, 4 — Musokhranovskaya anticline, 5 — Nikitinskaya syncline, 6 — Kalinovskaya anticline, 7 — Belovskaya syncline, 8 — Babanakovskaya anticline, 9 — Zainskaya syncline, 10 — Leninskaya syncline, 11 — Egozovskaya syncline, 12 — Mokhovo-Pesterevskaya anticline, 13 — Krasnoyarskaya syncline, 14 — Uropskaya anticline.

of the subsidiary sectors and mine fields have a homoclinal attitude with small dip angles. Second-order disjunctives are mainly confined to the boundaries of the distinguished scales; within the latter they are recorded much more rarely. But alongside comparatively simple areas, there is also a whole series of intricately structured sectors, characterized by a complex hypsometry of the coal seams caused by the presence of a large number of small folds and disjunctives.

Proceeding to consider the individual elements of the tectonics of the Leninsky district, one should first dwell on the characteristics of the forms of plicative dislocations. As was already indicated above, the principal forms of folds in the district are brachysynclines. Without going into a detailed description of the morphology and scale of each fold separately, we shall note only a number of their features. The most characteristic form of the district’s brachysynclines is represented by folds elongated along the southwestern boundary of Kuzbass, with broad, gently sloping bottom parts and rather steep limbs, whose dip angles not infrequently reach 60–70°, especially in the upper horizons at the outcrops of the seams beneath the cover deposits in the peripheral parts of the folds. This gives the brachysynclines of the district a characteristic trough-shaped form. The ratio of fold length to width is 2 : 1 in the Leninsky syncline, 3 : 1 in the Chertinsky, and 4 : 1 in the Belovsky. It is necessary to point out the asymmetric character of the brachysynclines. The axial planes of most folds have a steep southwestern dip, but the Toropovskaya and Egozovo-Krasnoyarskaya synclines have axial planes steeply dipping to the northeast. The axes of the brachysynclines have a distinctly wavy character in section. Their angles of plunge and rise average 2–8°, reaching the latter limit in the centriclines. It is characteristic that the plunge angles of fold axes in the northwestern centriclines are somewhat steeper: thus, in the Chertinsky syncline it is 8°, and in the Krasnoyarskaya 15°, as a result of which the maximum plunge of the bottom of the brachysynclines is displaced somewhat to the northwest. Along with bends of the axes in section, all of them in plan have a clearly curved S-shaped form. Thus, the axial line of the Belovsky syncline, having in the middle part of the fold a strike of about 320°, deviates sharply to the southwest in the southeastern centricline, while in the northwest, at the site of the anticlinal bend, it deviates to the east. As a result, the Belovsky and Nikitinsky brachysynclines proved to be arranged en echelon. Meanwhile, such an arrangement of brachysynclines is very characteristic in the district. As examples one may also cite the Nikitinsky and Kasminsky synclines, the Leninsky and Zainsky, and the Krasnoyarskaya and Egozovskaya synclines. In addition, a virgation of the axes of the district’s principal brachysynclines has been noted, leading to a considerable complication of the centriclines; examples here are the southern centricline of the Chertinsky syncline, and also the northern centricline of the Krasnoyarskaya syncline (Fig. 1). Thus, the behavior of the axes of the brachysynclines indicates rather complex conditions of deformation of the structure. The en-echelon arrangement of folds is also characteristic of intensely dislocated areas of Kuzbass.

Anticlinal folds, which in the district have a subordinate significance from the point of view of areal distribution, also have a brachyfold character. They, unlike the brachysynclines, are considerably more strongly elongated along the scales. These are mainly narrow folds with rather steep dip angles of the limbs, increasing toward the fold closures, which have an acute and cylindrical form. Most anticlines of the district are asymmetric, with the axial surfaces dipping to the southwest, with the exception of the Novorossiyskaya and Mokhovo-Pes-

of the [[unclear: ...]] anticlines, which have a northeastern plunge of the axial surfaces. The axes of the anticlines strike at an azimuth of 310–320°; however, the complex character of the bending of the axes in section and in plan leads to the fact that individual parts of the brachyanticlines assume a markedly diagonal position relative to the principal structures of the district. These include the Kalinovka anticline, which arose as a result of the eastward deviation of the axis of the Babanakovo anticline at the site of the anticlinal bend of the axis of the Belovo syncline. A complex character of axial bending is also noted in the Mokhovo-Pesterevo anticline, whose axis forms a distinct S-shaped bend in plan and a synclinal bend in section. Here one should also mention the Musokhranovo anticline, whose axis to the south turned sharply eastward at the site of the anticlinal bend between the Nikitino and Kasmin synclines. In general, the behavior of the axes of the anticlinal folds in many respects recalls and repeats the character of the axes of the brachysynclines. Despite the fact that the plicative structure of the district is substantially obscured by large disjunctives, it may be said that the synclines and anticlines have the same quantitative distribution and a close genetic and morphological connection, caused by the simultaneous development of negative and positive forms of dislocations. Concerning the general character of the folding of the Leninsky district, represented by an alternation of broad, gently dipping brachysynclines with steep limbs and narrow, steep anticlines, it may be said that in many respects it resembles the comb-like type of folding of V. V. Belousov [3].

The plicative structures of the first order described above are complicated by additional folding of higher orders. Among the latter several types may be distinguished. Most widespread within the district are transverse gentle waves that complicate the limbs and closures of the principal folds. The intensity of this type of additional folding is directly dependent on the character of the undulation of the axes of the large structures. Thus, within the Lenino syncline, which has large dimensions and smooth bends of the axis, the waves are gentle and broad; whereas the limbs and closure of the Egozovo syncline, with a more complex character of axial bending, are complicated by more frequent, narrow transverse folds. The dip angles of the transverse folds are small. Another type of additional folds consists of variously oriented small folds that developed at the sites of anticlinal bends of the axes of the principal brachysynclines. They are characterized by a fan-shaped arrangement of axial lines in plan and by rather considerable dip angles of the limbs, reaching 30–38° in the southern centricline of the Egozovo syncline (E. Yaroslavsky mine). In connection with the manifestation of this type of additional folding, the centriclines of most first-order structures have a complex hypsometry of the coal seams. An example is the northern centricline of the Krasnoyarka syncline, worked by the Gramoteino open-pit coal mine. Manifestations of additional folding also include overturns on the flanks of disjunctives of various orders.

Turning to the consideration of the forms of disjunctive dislocations, let us first consider the large ones, which determined the structure of the district as a whole. It should be noted that all of them, in general, are parallel to the boundary of Kuzbass and Salair, being longitudinal with respect to the principal plicative structures of the district. Their displacers strike at an azimuth of 315–325°, bending only slightly in plan. All first-order disjunctives that serve as the boundaries of scales have the character of reverse faults; and, since the bending of fold axes in the district is very considerable, the latter are often truncated by disjunctives. As a result of this—

the form of disjunctives changes repeatedly along the strike, giving conformable and nonconformable reverse faults, as well as reverse-fault forms of an indeterminate character, when the dips of the rocks on the hanging and foot walls of the disjunctive are opposite. All first-order disjunctives have a southwesterly dip; their dip angles vary within the range of 30–50° and do not depend on the dip angles of the strata they intersect. The displacement amplitudes of these disjunctives vary from 1000–1200 m at the Zhurinsky reverse fault to 1400–1500 m at the Kilchigizsky. One of the characteristic features of these disjunctives is the presence on their walls of thick zones of influence, within which it is practically impossible to correlate geological sections. The thickness of these zones differs for different disjunctives, and also varies along the strike of one and the same disjunctive depending on the nature of the relationship between the displacer and the strata it intersects. Thus, the thickness of the zones decreases in the case of longitudinal and conformable disjunctives and increases with other relationships of the displacer and the intersected rocks. The thickness of the zone of influence at the Zhurinsky reverse fault fluctuates within 200–300 m; at the Kilchigizsky reverse fault it reaches 1000 m. Since mining operations are not carried out in the zones of influence of large disjunctives, it has not been possible to study them in detail. However, observations of cores from exploratory boreholes show that the zone of the Kilchigizsky reverse fault is represented by intensely fractured rocks and tectonic breccias. Within this zone one can distinguish three or four small zones of especially intense rock disturbance, whose thickness varies from 25 to 85 m. The small zones are represented by crushed, brecciated, mylonitized rocks, crushed to tectonic clay. Numerous slickensides have been noted here. All this made it possible to suppose that the zone of influence of the Kilchigizsky reverse fault is represented by a series of parallel displacers. It should be noted that the entire zone described was formed in the hanging wall of the disjunctive. Such preferential development of zones of influence in the hanging wings is also characteristic of other large disjunctives of the district.

Among the disjunctives of higher orders, the Ursky reverse fault must first be considered. Work in recent years has established that this disjunctive has, according to V. I. Skok [4], a plicatogenic character, consisting in the close interrelation of the elements of occurrence of the displacer with the strata that it affects. This, in the opinion of V. I. Skok, indicates bending of the displacer, laid down at the early stages of formation of the plicative structure, together with the fold. Thus the displacer of the Ursky reverse fault, within the Novorossiysk anticline, forms an anticlinal fold, etc. Disjunctives of this kind have repeatedly been noted in the complexly dislocated areas of Kuzbass. In connection with the complex bending of the displacer of the Ursky reverse fault, various relationships arise between it and the rocks it intersects, as a result of which forms arise from a direct overthrust to a nonconformable reverse fault. The Ursky reverse fault is a regional, generally longitudinal disjunctive. The dip angles of its displacer, directly dependent on the occurrence of the elements of the folds that it intersects, vary within the range from 50–70° to 20–30°, decreasing to zero at the bends of the displacer. Despite the comparatively insignificant amplitude of displacement (150–300 m), the Ursky reverse fault is accompanied by a rather substantial (up to 300 m) zone of disturbed rocks, most significant in the hanging wall of the disjunctive, especially in those cases when the latter acquires the character of a nonconformable reverse fault.

Among other disjunctives of higher orders, the most numerous are those directly connected with disjunctives

of the first order and are their apophyses. A connection is observed between these dislocations and the main plicative structures of the district, with respect to whose limbs they are usually conformable. These are longitudinal or weakly diagonal conformable reverse faults, with displacement amplitudes along them from 100–200 to 30–40 m.

A special group should include the transverse East- and West-Kamyshan reverse faults, which developed on the northwestern limb of the Leninsky syncline within the fields of the E. Yaroslavsky (old) and S. M. Kirov mines. These structural forms have a northwestern dip at an angle of 20–35°. The amplitude of the first reaches 22 m, and of the second, 8 m. These disjunctives are evidently connected with transverse gentle folds affecting the limb of the Leninsky syncline.

Among the smaller disjunctives, which are not detected in the course of exploration work but have a significant influence during mining, the following principal groups may be distinguished: 1) small disjunctives that developed in the flanks of larger dislocations of the first and second orders. As a result of mining operations it has been established that these disjunctives are especially numerous in the hanging walls of dislocations, for example, the Zhurinsky reverse fault (field of the E. Yaroslavsky mine (old)). These structural forms are represented by longitudinal diagonal conformable and nonconformable reverse faults with amplitudes of up to 5 m. Their strike usually coincides with the strike of the main dislocation. Transverse reverse faults occur more rarely. The orientation of the dislocations of these disjunctives is determined by obliquely intersecting fracturing; 2) small disjunctives affecting the limbs of the main folds. Here the orientation of the dislocations is more complex. In relation to the axes of the folds on whose limbs they developed, most of the disjunctives are longitudinal. They form conformable and nonconformable reverse faults. On the southeastern limb of the Zhurinsky anticline (field of the “Zhurinka-3” mine), direct thrusts have been recorded. Among the disjunctives of this group there are steep (70–80°) transverse disjunctives with insignificant displacement amplitudes; 3) small locally developed disjunctives; the orientation of their dislocations does not constitute an exception to the general picture, but they have no clear association with larger disjunctives or folds. The displacement amplitudes of disjunctives of this group do not exceed 0.5 m.

Turning to the characterization of the jointing of coals and rocks, it may be said that it is not distinguished by great diversity. Within the district, two systems of normal-secant fractures are most widely represented—longitudinal and transverse with respect to the axes of the main plicative structures of the district, as was noted by I. I. Ammosov and I. V. Eremin [1]. In such complex nodes as centriclines, where additional folding and small disjunctives are concentrated, two systems of diagonal obliquely intersecting fractures appear, as well as a number of obliquely intersecting systems, among which one may distinguish longitudinal, transverse, and two or three diagonal ones. The same pattern is observed in the zones of influence of large disjunctives. Obliquely intersecting fractures also appear in the flanks of small disjunctives, which may serve as an indication of the appearance of the latter. Each complication of the structure, whether plicative or disjunctive, is accompanied by the appearance of fractures of obliquely intersecting systems.

From all that has been said here it is evident that the main tectonic elements of the Leninsky district as a whole are not distinguished by great complexity. However, despite the apparent simplicity of the structure, in the district there occur

areas where the combination of structural elements of different orders has created a rather complex tectonic picture. These include the mine fields of the E. Yaroslavsky Mine (old), the E. Yaroslavsky Mine, “Zhurinka-3,” and the areas of the Gramoteino open-pit coal mine. Complication of the tectonic structure is also quite possible in the Northern Nikitinsky area, where mine construction is planned. The close interrelation of supplementary structural elements with larger ones makes it possible to forecast the tectonics of areas subject to mining.

Literature

1. I. I. Amosov, I. V. Eremin. Fracturing of Coals. Publishing House of the Academy of Sciences of the USSR, 1960.

2. A. A. Belitsky, E. M. Pakh. Regularities in the tectonic structure of the Kuznetsk Basin. In: The Main Ideas of M. A. Usov in Geology. Publishing House of the Academy of Sciences of the Kazakh SSR, Alma-Ata, 1960.

3. V. V. Belousov. Fundamental Problems of Geotectonics. Gosgeoltekhizdat, Moscow, 1962.

4. V. I. Skok. Kemerovo District. Mineral Resources of the West Siberian Territory, vol. III, Novosibirsk, 1935.

5. M. A. Usov. Elements of the Tectonics of the Leninsky District of the Kuznetsk Coal Basin. Publishing House of the Administration of the State Association of the Coal Industry of the Kuznetsk Basin, Tomsk, 1923.

6. M. A. Usov. A geological-industrial sketch of the Kuznetsk coal basin. Proceedings of the West Siberian Branch of the Geological Committee, vol. VIII, issue 5, Tomsk, 1929.

7. M. A. Usov. Forms of disjunctive dislocations in the mines of Kuzbass. In: Collected Papers on the Geology of Siberia, Publishing House of the West Siberian Geological Prospecting Trust, Tomsk, 1933.